In prostate tissues of patients with BPH, the rise of steroid 5.alpha.-reductase activity in prostate tissue causes accumulation of the large amount of dihydrotestosterone (the product of steroid 5.alpha.-reductase). Hence, it was suggested that dihydrotestosterone plays an important role in the attack of BPH and that steroid 5.alpha.-reductase inhibitor is useful for the treatment of BPH [The Prostate Supplement 2: 95 (1989)]. It has been reported that the growth of prostate cancer is dependent upon dihydrotestosterone and is independent of testosterone so that steroid 5.alpha.-reductase inhibitor is useful for the therapy of prostate cancer [The Prostate 9: 343 (1986)]. Furthermore, it has been known that dihydrotestosterone plays a key role in the attack of acne and baldness.
The compound represented by the formula (A) shown below is disclosed as a synthetic intermediate of leukotriene antagonist in European Patent No. 290145. ##STR3##